Pressing "W" turned my cursor into a circle
In the new default Left Click Select keymap: 


right click (RMB) is what opens the menu for context-based special actions (Subdivide, Remove Doubles, etc), 

while instead
W cycles through the Selection tools from the Tools shelf




So now you've got Subdivide on RMB, and you can get your pointer back by hitting W 3 times.

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If you want to go back to Blender 2.79 Right Click Select keymap, you'll find this option in Edit > Preferences > Input > Select with.



The reason why everything else has disappeared is that you are in Local view (read that little (Local) in the Viewport's top left corner). I'm not sure how you entered this mode, and the W stuff is completely unrelated, but you can exit it using / or View > Local View > Toggle Local View